Alternative for old ika in Blender
Without using an armature you can use parenting and constraints.


Starting with two cylinders, add two empties. The empties should be located at opposing ends of each cylinder. 
Select a cylinder then Shift select the matching empty and parent them with &#9096; CtrlP -> Object. Repeat for other cylinder and empty.
Select a cylinder and add a TrackTo constraint. Set the target to be the empty of the opposing piston and set the axis to suit. Repeat for other cylinder.




Now as you move one of the empties the two pistons will always point towards each other. If you position one of the empties at the outer edge of a disc and parent the empty to the disc it will rotate around with it and the cylinders will follow.



Here is a sample file to look at.